1. Field of the Invention
The invention relates to a method and a device for spectral analysis of a useful signal or noise signal.
2. Related Technology
Analyzing a useful signal or noise signal with a spectrum analyzer or a noise-measurement station requires a spectral analysis over a broad frequency range. To achieve an efficient measurement of the signal or noise spectrum, the entire frequency range to be measured is subdivided into several frequency bands, each of which is measured with a different frequency resolution. For example, it may be meaningful to reduce the frequency resolution with an increasing frequency separation relative to the measured signal. As a result, lower-frequency frequency bands (frequency bands with a smaller frequency offset relative to the measured signal) are frequency measured with a higher frequency resolution than higher-frequency bands (frequency bands with a large frequency offset relative to the measured signal).
Modern spectrum analyzers typically operate according to the principle of superposition. With high frequency resolutions, the intermediate-frequency signal is sampled and subjected to a Fast Fourier Analysis (FFT). For low frequency resolutions, analog filters are used in the IF intermediate path and the analyzer is operated in a sweep mode.
With a spectrum analyzer operating according to the discrete Fast Fourier Analysis (FFT analysis), the total measuring time TMGes is obtained from the sum of measuring times TMi of the individual frequency bands. According to FIG. 1A, the measuring time TMi in each frequency band is once again composed of a multiple corresponding to the number of averagings of the additive combination of data-acquisition time TMesi—j and data-evaluation time TFFTi−j for the Fourier analysis with the addition of an averaging time TMiti and display time TDispi. The data-acquisition time TMesi—j in each frequency band is once again proportional to the frequency resolution of the respective frequency band. The total measuring time TMGes is therefore derived according to equation (1a).
                              T          MGes                =                                            ∑                              i                =                1                            M                        ⁢                                                  ⁢                          T              Mi                                =                                    ∑                              i                =                1                            M                        ⁢                                                  ⁢                          (                                                                    ∑                                          i                      =                      1                                        m                                    ⁢                                                                          ⁢                                      (                                                                  T                        Mesi_j                                            +                                              T                        FFTi_j                                                              )                                                  +                                  T                  Miti                                +                                  T                  Dispi                                            )                                                          (                  1          ⁢          a                )            
A reduction of the total measuring time TMGes can also be achieved according to FIG. 1B with a compact data-acquisition to be implemented repeatedly corresponding to the number of averagings and a subsequent compact data-evaluation by means of Fourier analysis to be implemented repeatedly corresponding to the number of averagings. The total measuring time TMGes is once again obtained according to equation (1a). Only a parallelization of the data-acquisition and data-evaluation by means of Fourier analysis leads to a reduction of the total measuring time TMGes according to equation (1b)
                              T          MGes                =                                            ∑                              i                =                1                            M                        ⁢                                                  ⁢                          T              Mi                                =                                    ∑                              i                =                1                            M                        ⁢                                                  ⁢                          (                                                                    ∑                                          i                      =                      1                                        m                                    ⁢                                                                          ⁢                                      (                                          T                      Mesi_j                                        )                                                  +                                  T                  FFTi                                +                                  T                  Miti                                +                                  T                  Dispi                                            )                                                          (                  1          ⁢          b                )            
Overall, a spectrum analyzer of this kind, which operates according to the discrete Fourier analysis in several frequency bands with different frequency resolutions, and which represents the prior art, provides an excessively long total measuring time by comparison. In particular, this excessively long measuring time is attributable to the intensive sequential data-acquisition for the individual frequency bands over several averagings. This sequential data-acquisition for the individual frequency bands leads to an intermittent time recording of the signal for the individual frequency bands, which disadvantageously necessitates a longer measuring time.